As known, the use of silicon for manufacturing opto-electronic devices is limited since the indirect band gap of silicon does not allow efficient photon emission. The doping of silicon with erbium ions can result in intense luminescence only at low temperatures, near the liquid nitrogen boiling point (77.degree. K). Moreover, it is known that the doping of silicon dioxide with erbium allows room temperature photo-luminescence. However, with erbium-doped silicon dioxide, it is not possible to observe luminescence produced by carrier transport (electro-luminescence) because of the insulating nature of silicon oxide.
Finally, a detailed analysis of the luminescence effects in erbium doped single crystal silicon indicates that opto-electronic application of this material is severely limited by the small solid solubility of erbium in silicon grown either by Czochralski or by float zone techniques.
Nowadays, photon-emitting devices are usually fabricated using compound semiconductors, such as GaAs or similar. However, technological processing of these materials is severely limited by the out diffusion of one of the constituents, which determines the loss of stoichiometry for thermal processes at intermediate temperatures. These materials, moreover, are not well suited for typical planar technology processes which are based on the properties of silicon dioxide. Diffusion barriers, insulating layers and all the other functions of silicon dioxide are replaced by deposited layers, characterized by physical-chemical performances which are worse than those of thermal silicon oxide.
Furthermore, the cost of compound semiconductor substrates is much higher than the cost of silicon wafers and the present production is unable to supply wafers whose size reaches the diameter of silicon wafers, currently of 200 mm. Such a limitation implies a smaller number of devices being fabricated in a single set of processes and thus still higher costs for each device.